1. Field of the Invention
2. Description of the Related Art
Pectate lyases, along with polygalacturonases and pectin lyases are enzymes that degrade pectin, a component of plant cell walls. Pectins are thought to act like a cement that holds adjacent cells together. Degradation of pectin plays a role in several normal developmental processes including: fruit ripening, pollen maturation, pollen tube growth and cell expansion and growth. Degradation of pectin is also a hallmark of several soft-rot diseases caused by both bacteria and fungi. Not surprisingly, pectate lyases are important virulence factors produced by several soft-rot pathogens. Therefore, the role of pathogen-produced pectate lyases in plant-pathogen interactions has been well studied. In particular, the pectate lyases (eels) of the soft-rotting Erwinia spp. have been well characterized. See Barras, F., F. Van Gijsegem, and A. K. Chatteijee1). Pels break the α-1,4-glycosidic linkages in pectate by β-elimination producing unsaturated products. Pels also require Ca++ for activity and function best at high pH, 8-9. PelA through PelE act as endo-pectate lyases with their final degradation products being short oligomers of galacturonic acid (di- to dodecamers) whose average length varies between Pels.
Plants also contain numerous genes homologous to pectate lyases. To date, two plant genes have been shown to have Pel activity when expressed in E. coli or yeast cells. One gene is primarily expressed in ripening strawberries and the other is expressed in a cultures of zinnia mesophyll cells that are differentiating into tracheary elements (See Domingo, C., et al.2. Also see Medina Escobar, N., et al.3). Pel activity was also demonstrated in cultures of zinnia cells in response to auxin or traceary element inducing media (See Domingo, C., et al.2).
In addition, Many pectate lyase-like genes are also highly expressed in mature pollen and are potent human allergens. Pet activity was demonstrated for a major pollen allergen of Japanese cedar, Cry j I (Taniguchi, Y., et al, Cryj I4). In contrast, researchers were unable to demonstrate Pel activity of Lat59 or Lat56, two tomato pollen-specific pectate lyase-like gene, expressed in a baculovirus expression system (Dircks, L. K., G. U. Y. Vancanneyt, and S. McCormick5). Therefore, it is possible that at least some of the Pel homologs found in plants may have activities other that degrading polygalacturonic acid and may utilize different pectic substrates.